GTK+ 2.x only looked up action *names* and ignored the namespacing offered by
action groups. This means that if there are two actions in different groups
with the same name, GtkUIManager may not find the one intended when it is
referenced in a menus definition file.
This commit changes that - if the action name contains a '/' character it is
assumed to contain both the action group name and the action name, and it will
only look for the action within the named group.
f82a9bbdc3